LONDON (Reuters) – A top investor in Barclays has launched the sale of a more-than 3% stake in the bank, the same day that the lender revealed a product sale blunder costing it an estimated 450 million pounds ($588.96 million). The institutional seller has instructed Goldman Sachs to sell 575 million shares in Barclays through a public bookbuild process, according to a Goldman Sachs note seen by Reuters. The sale is targeting a price range of 147.50 to 150.75 pence, representing a discount of 8.1% to 6.1% on today’s closing price, the note said. Barclays’ shares had already fallen 4% on Monday…